1. Field of the Invention
The present invention relates to a method for continuous manufacture of pasta products which may be readily rehydrated by immersion of the products in boiling or hot water for 1.5 to 5 minutes. The method includes the use of a preconditioner to partially pre-cook a flour and water mixture, and also includes the use of an extruder wherein the flour and water mixture is advanced first through a low temperature cooking zone, then through a venting zone and a forming zone, and finally through an extrusion die to yield the products. A significant amount of moisture is removed from the mixture in the venting zone thereby enabling use of greater amounts of direct injection steam into the mixture in the cooking zone without imparting excess shear into the pasta product which results in poor product integrity or adversely raising the temperature of the mixture to a value which would otherwise cause portions of the mixture to burn and form darkened specks in the extruded product.
2. Description of the Prior Art
Conventional pasta products are typically manufactured by uniformly combining water and flour such as Semolina and thereafter subjecting the flour and water mixture to extrusion under pressure through a die to shape the mixture into products of the desired shape, such as macaroni or spaghetti. However, conventional pasta products must be cooked for approximately 10 to 15 minutes in boiling water in order to hydrate and gelatinize the starch and transform the extruded product into an edible state.
In recent years, increased attention has been directed toward quick cooking pasta products which can be conveniently rehydrated in 3 to 5 minutes in boiling water. These products may also be mixed with other foods and cooked in a microwave or conventional oven without the need for precooking the products on a stove and thereafter draining the excess water.
U.S. Pat. Nos. 3,615,667, 4,230,735, 4,243,690, 4,423,082, 4,044,165 and 4,540,592 exemplify efforts which have been made in the past to improve the storage, cooking and visual characteristics of extruded, quick cooking pasta products. Attempts have also been made to decrease stickiness of the products, inhibit the formation of a slimy surface on the cooked product, and increase the integrity of the product with, of course, a minimum of manufacturing time and expense including overall energy costs during the extrusion process.
One particular problem which has been observed to occur during certain types of processes for extruding quick cooking pasta products has been the formation of black or darkened specks in the final manufactured product which decrease consumer acceptability and which may influence the taste of the product after rehydration. In this regard, it has been found that the darkened specks normally represent portions of the flour and water mixture which have temporarily adhered to the extruder screw flighting and have been burned as a result of the relatively high temperatures encountered during conventional, quick cooking pasta extruder processes. Such burned portions subsequently disengage the screw and are discharged through the die opening along with the remaining unburned portions of the mixture to thereby cause the dark specks in the final product which can be readily observed by simple visual inspection.
Furthermore, many of the known processes for manufacturing quick cooking pasta impose excessive amounts of shear on the flour and water mixture during advancement of the mixture through the extruder. Unfortunately, excessive shear of the flour and water mixture causes the final product to have a slimy surface and also decreases product integrity which is measured by the ability of the product to spring back to its original shape after rehydration. Moreover, excessive shear leads to increased extruder energy consumption and mechanical problems such as increased wear on the extruder components.
Hence, it would be desirable to provide a process for manufacturing quick cooking pasta at reduced temperatures in order to avoid formation of burned, darkened specks in the final product while, at the same time, the flour and water mixture are exposed to a minimum of mechanical shear during the extrusion process. Advantageously, such a process would overcome problems caused by practice of known methods such as formation of air bubbles in the extruded products and decreased product tolerance to overcooking. Desirably, the process would enable use of relatively high amounts of moisture during extrusion while reliably insuring that the extruded product is completely cooked before advancing toward a drying station where the products are dried during relatively short periods of time with air at ambient temperatures or temperatures somewhat above ambient.